The present invention relates to an external counterpulsation apparatus and method for controlling the same, more particularly, to an improved efficiency external counterpulsation apparatus and method for controlling the same.
External counterpulsation provides tangible curative effect in the treatment of cardiovascular diseases, which have become more and more prevalent in recent years. In American Cardiovascular Journal (30 (10) 656-661, 1973) Dr. Cohen reported a device for external counterpulsation, being a four-limb sequential counterpulsation device. It consists of multiple balloons wrapped around the four limbs of the patient. Pressure is applied sequentially from the distal to the proximal portion of each limb. Using high pressure gas from a large compressor as its energy source (1000 to 1750 mm Hg) to control the opening time of a solenoid valve, the balloons receive pressurized air during inflation. The balloons are deflated by use of a vacuum pump. The device requires the use of a large air compressor, a large vacuum pump and the use of numerous pressure transducers is to monitor the input pressure to insure that no excessive pressure is exerted in the balloons. However, this device is not only bulky and expensive, but is also extremely noisy and, complicated to operate. It is, therefore, unsuitable for everyday clinical use.
External cardiac assistance has been described in U.S. Pat. NO. 3,866,604, which is an improvement on the above original external counterpulsation device. However, this device is extremely bulky, noisy, and complicated to operate.
An external counterpulsation apparatus has also been described in Chinese Patent CN85200905, which has also been granted as U.S. Pat. No. 4,753,226. This external counterpulsation apparatus is regarded as another improvement over previous art. In addition to balloons for the four limbs, it also comprises a pair of buttock balloons. The balloons are sequentially inflated with positive pressure and then, with appropriate delay, simultaneously deflated using a microcomputer to control the opening and closing of solenoid valves. The high pressure gas source and vacuum pump have been eliminated, so as to reduce the volume of the apparatus and make it more practical. However, the deflation of the balloons of this apparatus lacks the suction of negative pressure and depends on natural exhaustion into the atmosphere. Therefore, the exhaustion of the balloons is incomplete and slow, and leaves behind residual gas in the balloon which hinders the ability of this device to reduce afterload (workload) of the heart.
A positive and negative enhanced type external counterpulsation apparatus has been described in Chinese Patent CN88203328, where a negative pressure suction means for exhaustion of the balloons has been added. However, this apparatus is still ineffective in the exhaustion of all the pressurized gas in the balloons, and in addition, it is still too large, noisy and heavy for transport to be of practical application in the clinical setting.
A miniaturized external counterpulsation apparatus has been described in Chinese Patent CN1057189A, wherein the air compressor can be placed inside the main body of the device and does not require a separate embodiment. The box containing the solenoid valves and the balloon cuffs are suspended in a tube like aparatus and directly attached to the main body of the device. This device is practical for clinical use in that its size is very much reduced. However, this device does not have negative suction increase the rate of deflation of the balloons, and it is still extremely noisy and not very efficient in producing desirable counterpulsation hemodynamic effects, namely, a high rate of inflation and effective deflation.
The foregoing external counterpulsation apparatuses have many advantages over the original one, but there are still many problems. For example, the high pressure air produced by the air compressor has a high temperature when it arrives at the balloons, which may feelings of discomfort or even pain for the patient; the balloon cuff used by the prior art external counterpulsation apparatus is made of soft materials such as leatherette, canvas and the like, which may have a high elasticity and extensibility, requiring the use of a large volume of gas to achieve the required pressure and resulting in the inability to quickly inflate the balloons for optimal rate of inflation. Furthermore, dead space may be formed due to the misfit between the balloon cuff and the surrounded limb; the balloon cuff could slip downward during counterpulsing thereby being incapable of efficiently driving blood from peripheral regions to the root of the aorta, which directly affects the effectiveness of the counterpulsation treatment. All these factors reduce the efficiency of counterpulsation and require more pressurized gas to fill up dead space and more power from the compressor. At the same time a reduction in the rate of inflation of the balloon results in hindering the effective compression of the body mass as well as vasculature.
Historically, the earlobe pulse wave, finger pulse or temporal pulse wave are used as a timing signal to give the appropriate time for application of the external pressure so that the resulting pulse produced by external pressure in the artery would arrive at the root of the aorta just at the closure of the aortic valve. Thus, the arterial pulse wave is divided into a systolic period and a diastolic period. However, earlobe pulse wave, finger pulse wave of temporal pulse wave are signals signal derived from microcirculation and may not reflect the true pulse wave from the great arteries such as the aorta. Using the dicrotic notch as the true aortic valve closure is incorrect because the dicrotic notch is affected by many other factors such as the dampening effect of the vascular elasticity, reflective wave from tapering of the arteries and interference from previous pulse waves. Therefore, it is most important in the art of external counterpulsation to find the true aortic valve closure time so the appropriate inflation time can be found for the externally applied pressure.
Theoretically, there are two factors that should be taken into account to determine the appropriate deflation time of all the balloons simultaneously: (1) release of all external pressure before the next systole to produce maximal systolic unloading, that is the maximum reduction of systolic pressure; (2) maintainence of the inflation as long as possible to fully utilize the whole period of diastole so as to produce the longest possible disatolic augmentation, that is the increase of diastolic pressure due to externally applied pressure. Therefore, one measurement of effective counterpulsation is the ability to minimize systolic pressure, and at the same time maximize the ratio of the area under the disatolic wave form to that of the area under the systolic wave form. This consideration can be used to provide a guiding rule for determination of optimal deflation time.
Furthermore, the various existing external counterpulsation apparatuses only measure the electrocardiographic signals of the patient to guard against arrhythmia. Since counterpulsation applies pressure on the limbs during diastole, which increases the arterial pressure in diastole and makes it higher than the systolic pressure, the blood flow dynamics and physiological parameters of the human body may vary significantly. Some of these variations may be advantageous, while some of them are potentially unsafe. For patients with arteriosclerosis and phlebosclerosis, there is the danger of blood vessels breaking due to the increase in their internal pressure. Furthermore, applying pressure to the limbs presses not only on the arteries but also the veins, and this may result in an increase in the amount of blood returning to the heart. This may cause cardiac lung or pulmonary edema because of the degration of the the decrease in pumping capacity of the heart and incapability of the heart to pump out the increased amount of blood returning to the heart. This may, in turn, affect the oxygen saturation in the arteries of the body and cause an oxygen debt. It is, therefore, necessary to monitor the maxiumum value of the arterial pressure and oxygen saturation in the blood of a patient in addition to monitoring the electro-cardiogram, to ensure safety of the patient during the counterpulsation treatment.
Furthermore, the gas distribution device in the existing external counterpulsation apparatuses operate by controlling the opening and closing of the solenoid valves, which has the disadvantage of having voluminous and complex pipe connections. This is disadvantageous to miniaturizing the whole apparatus and improving its portability.
Accordingly, it is an object of the present invention to overcome the above disadvantages and provide an improved efficiency external counterpulsation apparatus.
It is another object of the present invention to provide an external counterpulsation apparatus having accurate and reliable timing of inflation and deflation and reduced temperature of the pressurized gas, such that the gas flow temperature of the balloons is near to room temperature.
It is a further object of the present invention to provide a miniature external counterpulsation apparatus having a new gas distribution means and reduced pipe connections.
It is yet another object of the present invention to provide an external counterpulsation apparatus having devices for monitoring the blood pressure and oxygen saturation in the blood of a patient, and to monitor other complications araising from the treatment.
It is yet another object of the present invention to provide a negative suction to the deflation of the balloons so as to effectively exhaust all pressurized gas rapidly, to lower the systolic pressure, and reduce the noise level of the solenoid valves.
It is yet another object of the present invention to provide a semi-rigid or rigid balloon cuff which can either be molded into the shape of the surrounded limb, or used in conjunction with inserts of suitable incompressible materials used to occupy the dead space between the balloon cuff and surrounded limb to effectively reduce the volume of compressed gas and power loss as well as the time required to raise the external pressure to the required level for compression of the underlying vasculature.
It is a further object of the present invention to provide a more effeicient compressor for the use of external counterpulsation to produce the right volume of gas at the appropriate pressure, and which has reduced size, noise level and electrical power consumption.
To achieve the above objects of the invention, the present invention proposes an external counterpulsation apparatus, which comprises:
a first gas compressor;
a second gas compressor;
a control means;
a first positive pressure reservoir;
a second positive pressure reservoir;
a first negative pressure reservoir;
a second negative pressure reservoir;
a first solenoid valve;
a second solenoid valve;
a plurality of balloon devices, each of the balloon devices consisting of a balloon and a balloon cuff body which is made of a material of certain toughness and hardness, and fixing elements, wherein the shape of the balloon cuff body substantially matches the contour of the upper or lower limbs or the buttocks of the body;
a gas distribution means, comprising a cylinder and corresponding piston; a partition in the cylinder having a central hole therein which divides the cylinder into two portions, the piston also being divided into two portions, a first portion and a second portion, positioned one on each side of the partition, the two portions being connected by a rod passing through the central hole of the partition; a plurality of vents corresponding to said plurality of balloon devices which are symetrically arranged on two sides of a first portion of the cylinder, each of the vents being connected to a corresponding one of the plurality of balloons of the balloon devices by pipes; an outlet in this portion of the cylinder, which is connected to the first negative pressure reservoir by a pipe and to the second negative pressure reservoir via the second solenoid valve; the second portion of the piston is of an xe2x80x9cIxe2x80x9d shape and forms a cylindrical gas chamber within the cylinder, the axial length of the gas chamber being selected so that it communicates with each one of the symetrically arranged vents as the piston moves, towards the first portion of the cylinder; a first vent, a second vent in the second portion and a third vent in the first portion of the cylinder, wherein the first vent is connected to the first solenoid valve by a pipe, the piston being movable towards the first portion of the cylinder when gas is flowing from the first positive pressure reservoir into the cylinder via the first solenoid valve, the second vent being positioned between the first portion of the piston and the partition and also being connected to the first solenoid valve by a pipe so that gas may flow from the first positive pressure reservoir into the gas chamber and move the piston in the opposite direction towards the second portion of the cylinder; the position of the third vent is selected such that whatever position the piston is in, the vent will always communicate with the gas chamber formed by the second portion of the piston and the cylinder, the third vent is connected to the second positive pressure reservoir by a pipe; gas flow can sequentially inflate the plurality of balloons via the plurality of corresponding vents in the first portion of the cylinder as the piston moves across the plurality of vents; the outlet in the first portion of the cylinder being connected to the negative pressure reservoir by a pipe; when the balloons deflate the second solenoid is opened, and the gas in the balloons is discharged into the second negative pressure reservoir while discharging into the first negative pressure reservoir;
a control means, including a plurality of detector electrodes positioned at predetermined places on the body, a high frequency constant current source, filter means for electrocardiographic and impedance signals, and a computer system consisting of a micro-computer and A/D convertors, the computer system operating to perform adaptive filtering of the impedance cardiograph, to obtain data for controlling the inflation and deflation time of the balloons, and to generate corresponding inflation and deflation signals; a drive circuit, responsive to said inflation and deflation signals, operating to automatically inflate and deflate the balloons, and to discharge of the gas in the negative pressure reservoirs.
Preferably the counterpulsation apparatus of the present invention also comprises a blood pressure detector means, for monitoring the blood pressure of the patient during counterpulsation comprising; solenoid valves and throttle valve for inflating and deflating the cuffs, electromagnetic pressure transducers for sensing pressure inside the cuffs, electrophoto-transducers for measuring pulse wave and oxygen saturation of blood, and an emplifying and filtering processing circuit. The maximum blood pressure of the artereal pressure is monitored by a cuff occlusive indirect blood pressure measuring method. At the beginning of measurement, the inflating passage of the solenoid valve is opened, gas for pressurizing the lower limbs inflates the cuffs via pipes and solenoid valves. Pressure transducers monitor the pressure inside the cuffs. When the pressure rises to a certain value after occlusion of the arteries and the electrophoto-transducer can not detect the pulse wave, the solenoid valve opens the deflating passage and the gas in the cuffs slowly deflates via the solenoid valves and the throttle valves and the pressure inside the cuffs slowly drops. When the pressure inside the cuffs is equal to or slightly below the maximum pressure of the arteries (which is the systalic pressure before counterpulsation, and diastole counterpulsation pressure during counterpulsation) the occluded blood vessels are pushed open instantaneously, at that time, a rapidly varying pulse wave can be detected by the electrophoto transducer, which indicates the arrival of the maxiumum pressure of the arteries. The pressure detected by the pressure transducer at that time is the maxiumum pressure. The apparatus preferably also includes a blood oxygen detector means, for monitoring the oxygen saturation in the blood during counterpulsation by the use of pulse blood oxygen measuring method. The transducer for pulse blood oxygen measurement cooperates with the electrophoto-transducer for detecting pulse waves in blood pressure measurement, and after amplifying and filtering, processing the saturation of blood oxygen is obtained by analyzing and calculating of the waveform by the micro-processor. When the blood pressure exceeds a predetermined value, or the blood oxygen saturation goes below a predetermined value, the computer issues a signal to stop the counterpulsation.
In addition, the present invention provides a method for controlling the external counterpulsation apparatus, comprising the steps of:
(a) obtaining an impedance cardiograph during counterpulsation with stable waveform and the distinct characteristics such as the closure of the aortic valves using a plurality of electrodes and self-adaptive filtering technology;
(b) performing self-adaptive filtering processing and detecting of the impedance cardiograph by the use of a micro-computer to obtain the closing point of the aortic valves and the starting point of the counterpulsation wave. The proper inflation time of the balloon cuffs can then be accurately determined by moving the starting point of the counterpulsation wave to coincide with the aortic valves closing time. In case there is too much noise in the impedance cardiograph such that determination of the aortic valves closure is impossible, then the inflation will be set at the end of the T wave of the electrocardiogram or using the method described in U.S. Pat. No. 5,753,226.
(c) Using impedance cardiograph to detect the peak amplitude and duration of the systemic systolic blood pressure and the amplitude and duration of the pulse wave created by comterpulsation to calculate objective index such as the ratio of peak diastolic to peak systolic blood pressure as well as the ratio of the area under the systolic and disatolic pulse wave as indications of the hemodynamic effectiveness of counterpulsation; and
(d) The ability to determine the ratio of the areas under the diastolic and systolic pulse waves provides means to adjust the deflation time in such a way as to maximize this ratio. However, the adjustment of the deflation time in maximizing the reduction of the systolic blood pressure is more important than maximization of the ratio under the diastolic and systolic pulse wave; and
(e) controlling the inflation and deflation times of the external counterpulsation apparatus with a computer
Preferably, the method may also comprise the steps of:
(f) detecting the blood pressure state of the patient with a blood pressure detector means during counterpulsation to improve safety, and stopping counterpulsation when the blood pressure exceeds a predetermined valve; and
(g) detecting the blood oxygen saturation of the patient with a blood oxygen detector means during counterpulsation to improve safety, and stopping counterpulsation when the oxygen saturation goes below a predetermined level.
The advantages of the present invention lie in reduced gas consumption and effective counterpulsation, thereby reducing the burden on the gas compressor. In addition, discomfort or pain to the patient is reduced, and the burden on other environmental conditions is reduced as well, while the portability of the counterpulsation apparatus can be increased. Another significant advantage of the present invention lies in the non-invasive detection of the maximum arterial pressure and oxygen saturation of the blood of the patient, thereby guaranteeing the safety of the patient during counterpulsation treatment. And, more importantly, new control means and methods are adopted by the present invention, which make the inflation and deflation times of the counterpulsation apparatus more accurate and reliable, and improve the safety levels of counterpulsation treatment.